Contamination of surfaces with microoorganisms can cause problems in a number of areas. For example, microorganisms which are injurious to health may be present on a surface on which food is prepared. If these organisms are transferred to the food, illness can result for a person who consumes the food. Further problems are caused by microbial contamination of the inner walls of air-conditioning ducts or water supply pipes within buildings, or by contamination of devices for use in or on the human body, for example, contact lenses, surgical instruments etc. These problems not only include the risks to health but also, especially in the case of pipes and the like, increased fluid frictional resistance, increased heat transfer resistance and biocorrosion. Many other examples are apparent from the literature and could be cited.
Many compositions are known and used for the cleaning and disinfection of surfaces. Almost all these compositions share the common feature that they contain a hygiene agent which is toxic to or inhibits the growth of microorganisms. Typical hygiene agents include, strong acids, alkali's, phenolics, oxidising agents such as peracids and hypohalides and charged species such as cationic surfactants. These are generally highly reactive species which exhibit this reactivity in terms of one or more of, short shelf life, toxic, corrosive and irritant properties and, in general, these components are required at relatively high levels in formulations to obtain a satisfactory result.
In many circumstances microorganisms will grow on a surface to form a confluent or part-confluent biofilm. Bacterial biofilms are regarded as problematic in household and industrial hygiene as well as in medicine where they can act as reservoirs for spoilage organisms or pathogens or can lead to so-called biofouling. Biofilms are regarded as problematic in infections associated with indwelling medical devices and other articles in contact with wet body tissues, such as contact lenses.
Conventional approaches to the control of biofilms, such as the application of the hygiene agents described above have demonstrated that these films are recalcitrant. A number of factors are thought to contribute to this recalcitrance, and it is believed that a major factor is the ability of the glycocalyx, an extracellular polymer of polysaccharides and glycoproteins to react with highly reactive species, such as the above mentioned oxidising agents or halogens and to bind the above mentioned charged species. It is believed that these interactions prevent effective access of the hygiene agent beyond the exposed surface of the biofilm.
It is known that the activity of certain hygiene agents can be improved by addition of other components. For example, the reaction of hypochlorite solutions with strong acids will produce chlorine a potent, if somewhat dangerous, hygiene agent. It is also known to generate hygiene agents by catalytic action. EP 0436466 discloses a method of disinfecting a hydrogen peroxide stable material by contacting said material with a hydrogen peroxide containing solution and a hydrogen peroxide decomposition means such as a catalyst on a separate support.
WO 93/00815 discloses how it is possible to bind a photosensitiser to a surface which is capable of catalysing the formation of singlet oxygen from triplet oxygen under the influence of visible light, thereby providing photobacterial properties and an autosterile character to the surface upon exposure to visible light. Compositions for use in such a method comprise 0.1-1.0% by weight of the photosensitiser, which may be a porphyrin or phthalocyanine, preferably in the unmetalled form. Salts of the meso-tetra(N-octyl-4-pyridinium)porphyrin tetracation are known to have both cytotoxic and phocytotoxic properties. Similar techniques are known for the preparation of ceramic tiles and other such sanitary ware. In such systems, as disclosed in the trade literature of Toto Ltd of Minato-Ku, Tokyo, photoactivation of a compound based on titanium dioxide is believed to produce an excited species which is effective as a hygiene agent.
A disadvantage of the photochemical systems is that they are less effective or ineffective under low light conditions or in the dark. Given that many of situations in which microbial contamination can occur are not well lit (such as the inside of air-conditioning ducts or water supply pipes) there is a need to provide hygiene systems which are effective against biofilms, both in lit and dark conditions without requiring the use of high levels of reactive hygiene agents.